Transcript for Dog Flipping: 7 Million Dogs and Cats are Lost Every Year

And now something that may have you holding your dog leash closer tonight. A new kind of thief, called a dog flipper, and a new kind of pet detective determined to bring your puppy home. Abc's alex perez. Reporter: Liz arroyo was a bundle of nerves when her dog raiden went missing last month. He's like my baby. He's a part of the family, you know. Reporter: Arroyo sent picture of raiden to danielle beck, a pet detective whose website helps reunite missing animals with their owners. Her site's followers scoured the web, matching up nose lengths, whiskers, ears. Soon finding this ad on craigslist, those yellow eyes, that unusual mix. Price tag -- $1,000. Beck identified it as a likely case of flipping. What is this idea of dog flipping? That I either finding the dog or stealing the dog from someone. Then they're turning it around and they're saying they're rehoming the pet, but they're selling somebody else's pet. Reporter: Beck alerted arroyo who answered the ad. You knew right away, this is my dog? Right away. There was absolutely no question. Reporter: When she called, the apparent flipper told her that she'd had him for six months. Arroyo told the womashe'd need to go to an atm for cash. Instead she returned with the police. Reporter: As soon as you come back with a police officer, her story changes? Yes, and she wouldn't even look me in the eye either. There was little police could do. Selling a pet is not illegal unless it's stolen and proving that is very difficult. So how can owners protect their pets? Make sure they are spayed or neutered. Dogs or cats that cannot breed are less valuable. And have them micro chipped. More than a million reunions between owners and their micro chipped pets have been documented. Liz arroyo and raiden had their reunion too, a story that could have had a very different ending. Alex perez, abc news, indianapolis.

This transcript has been automatically generated and may not be 100% accurate.

{"id":19858105,"title":"Dog Flipping: 7 Million Dogs and Cats are Lost Every Year","duration":"2:08","description":"Missing animals are bought and sold online, but this pet detective helps them find their way home.","url":"/WNT/video/dog-flipping-million-dogs-cats-lost-year-19858105","section":"WNT","mediaType":"default"}